1. Field of the Invention
The present invention relates to a process for preparing polyamide elastomers having rubbery elastic properties and excellent low-temperature resistance and recovery.
2. Description of the Prior Art
Recently, a thermoplastic elastomer having a so-called micro-phase separation structure, i.e. having a soft segment which exhibits a soft, rubbery elasticity and a hard segment which exhibits a hard, aggregated domain by forming physical crosslinkings according to a mutual action, such as crystallization or hydrogen bonding, in the molecular chain, has attracted attention, since the following facts have been found: the thermoplastic elastomer can be molded by a process generally employed for molding thermoplastic resins; substances widely ranging from a rubbery substance to a plastic substance can be obtained easily by suitably selecting the soft segment-forming and the hard segment-forming components; and the micro-phase separation structure of this material has special properties such as antithrombatic activities, membrane separation functions and adhesiveness.
The soft segment-forming components of the thermoplastic elastomers preferred from the viewpoint of low-temperature properties are polyoxyalkylenediols such as polyoxyethylene glycol, polyoxy-1,2-propylene glycol, polytetramethylene glycol, block or random copolymers of ethylene oxide and propylene oxide, and block or random copolymer of ethylene oxide and tetrahydrofuran. Among them, polyoxytetramethylene glycol is recommended from the viewpoint of its thermal resistance, water resistance, low-temperature properties, elastic recovery and mechanical strength. This compound is now in use as the soft segment-forming component for polyurethane, polyester elastomers and polyamide elastomers. For example, polyamide elastomers prepared by using polyoxytetramethylene glycol as the soft segment-forming component have been disclosed in the specifications of Japanese Patent Laid-Open Nos. 159586/1975, 12297/1977, 119997/1978, 126057/1978, 1298/1978 and 119925/1982.
However, when the polyoxytetramethylene glycol having a molecular weight exceeding a certain value is used, crystallization is caused in the soft segment due to its linear structure and, therefore, the properties thereof such as low-temperature properties and elastic recovery are not always satisfactory.